Type II Superlattices for LWIR Detectors and Focal Plane Arrays

Long wavelength infrared (LWIR) detectors are highly needed for night vision and threat warning applications. The InAs/GaSb Type II heterostructure system offers unique design flexibility for new innovative detectors. Type strained layer superlattice (SLS) detectors have been demonstrated with cutoff wavelengths ranging from 3 to 32 microns. This technology has shown performance comparable to HgCdTe in the MWIR and LWIR ranges, but there is still much work to be done to accomplish full commercialization. It is proposed to demonstrate Type II superlattice detectors with improved performance similar to or better than existing HgCdTe technology in the LWIR range. Several tasks are required to improve Type II LWIR sensors: (i) Design of a suitable structure with cutoff wavelength in the LWIR at the desired operating temperature, as well as incorporating novel designs for higher differential resistance/quantum efficiency (ii) Optimization of the epitaxial growth conditions for LWIR superlattice material with the goal of minimizing recombination centers, (iii) Device fabrication, and (iv) Device measurement and analysis to determine dark current mechanisms and methods for reducing them. This data would then be applied back to steps (i)-(iii) to further improve performance.